The invention relates to resonant tag labels which are used in electronic article surveillance and identification systems.
Conventional electronic article surveillance systems are utilized widely as an effective deterrent to unauthorized removal of items from specified surveillance areas. In surveillance systems of this type, articles to be monitored are provided with resonant tag labels which are used to detect the presence of the articles as they pass through a surveillance zone. The surveillance zone typically comprises an electromagnetic field of a predetermined frequency generated in a controlled area. The tag label resonates at the frequency of the electromagnetic field or another predetermined frequency. The resonant frequency is detected by the system and provides an alarm indicating the presence of the label and, therefore, the article. For deactivation, a strong surge current is induced in the resonant tag label in order to produce a short-circuit.
Presently available resonant tag labels include conductive layers separated by a dielectric layer. Specifically, such labels include circuits having a dielectric carrier film with an inductive spiral applied to one side thereof, such as an appropriately configured metal foil, which is terminated at each end by first and second conductive areas. Matching conductive areas are applied to the opposite side of the dielectric carrier film to form a capacitor, thus completing an inductive-capacitive tuned resonant circuit. The circuits may also be configured such that a direct electrical connection is provided between the conductive areas on both sides of the dielectric film.
Label thickness is increased significantly by the reliance on relatively thick films as the dielectric medium for physically separating and supporting the conductive components of the circuit. Thickness is further increased by the application of additional films or coatings to protect and stabilize the label. The resulting overall thickness of the labels makes it difficult if not impossible to effectively conceal them from detection and unauthorized removal by those determined to foil the surveillance system.
With respect to identification systems, conventional methods typically involve automatic reading of bar codes (UPC) provided on indicia receptive labels. Unfortunately, a disadvantage in bar code systems includes the need for the article to which the label is applied and the bar code itself to be oriented such that the reading or detection beam can properly read the bar coded information. This problem can be serious if the objects being identified are to be sorted and the objects are random as to delineation and orientation.
It is therefore an object of the present invention to provide a resonant tag label which is constructed with thin coatings so that the tag label may be disguised, for example, underlying a conventional printed label.
It is a further object of the present invention to provide a resonant tag label and method for making same which utilizes a minimum of components and which is separable from an initial film used primarily during the configuration of the tag label.
It is yet another object of the present invention to provide a resonant tag label which is responsive to a plurality of frequencies.
It is an additional object of the present invention to provide a resonant tag label which provides proper electronic identification information regardless of the orientation of the label.
It is yet another object of the present invention to provide a thin, frangible resonant tag label which in essence requires a substrate film or a substrate object to which it is applied in order to remain a viable construction.